The present invention relates to auxiliary axle assemblies for vehicles used to transport heavy loads, and more particularly to systems for mounting and operating the auxiliary axle assemblies.
Auxiliary axles, also known as tag axles, booster axles, and swing-frame axles, traditionally are employed in concrete transit mixers, gravel trucks, refuse hauling trucks and other vehicles used to haul heavy loads. The wheels of the auxiliary axles are mounted to a frame including transversely spaced apart pivot arms. The arms are attached rotatably to opposite longitudinal rails or frame members of the vehicle chassis whereby the frame can pivot relative to the vehicle chassis between a lowered position with the wheels engaging the ground, and a retracted position in which the wheels are supported above the ground. A hydraulic cylinder, coupled between the chassis and the frame, is extensible and retractable to alternatively lower and raise the frame and wheels.
Tag axle assemblies are useful in terms of increasing the actual and legal (weight per axle) load carrying capacity, and can improve balance and stability, mainly by increasing the distance between the most forward and most rearward axles during transit.
The pivotal couplings of tag axle frames with vehicle chassis are subject to severe environmental conditions occasioned by exposure to dirt and grime, shock, vibration and other applied loads during transit and on the job site, and exposure to chemicals such as the acid wash used to clean concrete transit mixers. Accordingly, manufacturers have attempted to provide tag axle systems designed for easier access to pivot joints for maintenance, repair, and replacement. Examples of this approach are shown in U.S. Pat. No. 5,897,123 (Cherney et al.), and U.S. Pat. No. 6,135,469 (Hulstein et al.). In U.S. Pat. No. 7,175,189 (Eull), a booster axle mounting system includes brackets attached to a truck frame, a pair of pivot bearings secured to forward ends of booster axle assembly arms, and a pair of pivot pins, each connecting one of the pivot bearings to one of the brackets. The pivot bearings are welded to the axle frame arms.
U.S. Pat. No. 6,478,317 (Konop) discloses a pair of pivot joint units for coupling an auxiliary axle assembly to the rails of a vehicle chassis. Each unit includes a bracket removably bolted to one of the chassis rails and supporting a bushing and pivot pin. Dual prong connectors are fixed to a forward portion of an auxiliary axle frame, and removably coupled to the pivot pins. This arrangement is said to provide removable and replaceable pivot joints and provide no pivotal wear parts that are permanently attached to the chassis.
Although the foregoing approaches may afford several advantages, they are subject to the risk of improper assembly inherent in systems that contemplate repeated disassembly and reassembly for maintenance, repair, or replacement of components. As an example, the bolts used to secure the brackets to the chassis rails must be tightened to the proper torque or bolt tension to integrally secure the brackets without unduly stressing or otherwise damaging the bolt or nut. Although factory settings involve proper bolt tensioning, there is no assurance that repeated bracket mountings after disassembly for inspection, repair, etc. will entail the same level of care to ensure proper tensioning. Further, because the bracket-supporting bolts are not permanently secured, they may become loose when subject to shock and vibration of components during transit and at the job site.
Therefore, the present invention has several aspects directed to one or more of the following objects:                to provide an auxiliary axle system that is easier to maintain due to a permanent installation of components mounted removably in previous systems;        to provide an auxiliary axle mounting apparatus capable of accommodating different transverse distances between vehicle frame members;        to provide a process for equipping a vehicle chassis to pivotally support an auxiliary axle frame in which longer lasting components are permanently installed to enhance system reliability and useful life; and        to provide an auxiliary axle system in which durable bushings are advantageously employed to rotatably couple the auxiliary axle frame to the chassis, and to a cylinder used to controllably raise and lower the frame.        